Developing apparatus

ABSTRACT

Developing apparatus wherein an electroscopic marking particle loaded applicator is moved to develop charge patterns, the applicator having such a configuration that in a first or developing position it effects deposition of the marking particles on the patterns and in a second or viewing position it does not obstruct direct viewing of the developed patterns.

11 uited States Robinson, Jr.

atent [1 [11 3,811,766 [451 May 21, 1-974 DEVELOPING APPARATUS [75] Inventor: Thomas K. Robinson, Jun,

Rochester, NY.

[73] Assignee: Xerox Corporation, Rochester, NY.

[22] Filed: Mar. 10, 1969 [21] Appl. No.: 805,694

[52] US. Cl. 355/3, 117/175, 346/74 ES [511 int. Cl 603g 15/00 [58] Field'of Search 5/3, 10, 17; 117/175; 346/74 ES [56] References Cited UNITED STATES PATENTS 3,232,190 2/1966 Willmott 355/3 2,919,171

12/1959 Epstein 34 6/74 ES 3,167,166 1/1965 Schiebeler 346/74 E X 3,484,792 12/1969 9 3,288,605 11/1966 3,372,027 3/1968 Gundlach 355/10 X Primary Examiher-Monroe H. Hayes 57 ABSTRACT Developing apparatus wherein an electroscopic marking particle loaded'applicator is moved to develop charge patterns, the applicator having such a configuration that in a first or developing 'position'it effects deposition of the marking particles on the patterns andjin a second or viewing position it does not obs'truct direct viewing of the developed patterns.

.10 Claims, 5 Drawing Figures PATENTEUHAY 2 1 i914 SHEET 1 OF 2 'INVENTOR. THOMAS K. ROBINSON JR ATTORNEY PATENTEnmm an sum a nr 2 CHAR GENERATOR l Fm PRINTER v DELAY FIG.

DECODER 0 fiwa KEYBOARD 72 COUNTER l DEVELOPING APPARATUS This invention relates generally to developing apparatus, and specifically to'apparatus for rendering electrostatic charge patterns visible by depositing electroscopic marking particles thereon.

Ever since the advent of electrography, or the act of placing electrostatic charges on an insulating recording medium using conductive electrically biased electrodes or styli and rendering these charges visible, efforts have been directed to finding applications to which this new art could be put. Such endeavors produced high speed computer printer terminals,communications printers, label printers, facsimile machines and many special purpose apparatus where the advantages of electrography were essential. I

One application which has not yet been exploited is that of a very low speed printer which is capable of competition with the conventional office impact typewriter. Workers in the electrographic arts attribute this failure to many different reasons, But one reason which is generally cited in common is the present inability to meet the condition of instant visibility of the printed information.

By instant visibility" it is meant that'as a single alphanumericsymbol or characteris recording in the form of a latent electrostatic image or pattern it is developed or rendered visible before or during the recording of another character. This capability is critical to the success of any keyboard input printer terminal since the operator is most desirous of seeing what he or she is typing. This desire stems from both an operational need, viz., to detect errors, and a psychological need, viz., to occupy the eyes when entering information via the keyboard from a written message. The second need can be better appreciated when it is considered that by nature a keyboard operator is unaccus tomed to typing without a visual indication of the results of this operation. By the term typing it is meant I to select and depress or otherwise actuate a key on a keyboard for purposes of information recording or transmission.

Conventional impact typewriters accommodate the aforementioned needs of the typist by moving a carbon or inked ribbon up and into position between the paper and type piece for recording and then returning the ribbon down to a position which does not obstruct the typists view of the last recorded character.

However, the electrographic process necessitates development of the electrostatic charge pattern which is improve electrostatic'charge pattern development.

Another-object of the present invention is to provide novel development apparatus for electrostatic patterns which permitsrapid viewing of the developed patterns.

. These objects and others that may be apparentare achieved in accordance with the principles of the present invention wherein an electroscopic marking particle loaded applicator is moved to develop charge pat- 2 terns, the applicator having such a configuration that in a first or developing position it effects deposition of the marking particles on the patterns and in a second or viewing position it does not obstruct direct viewing of the developed patterns.

Other features and advantages of the present invention may become more apparent from reading the following .detailed description in connection with the appended drawings wherein:

FIG. 1 is a perspective view of one embodiment of the present invention with broken away portions in an electrographic printer;

FIG. 2 is a cross-sectional view of the present invention as employed in a printer; Y

FIG. 3 is a block schematic of a typical control system for the present invention;

FIG. 4 is a perspective view of another embodiment of the present invention; and

FIG. 5 is another view of the embodiment of FIG. 4.

As is well known, electrograph'y may be defined as the deposition of electrostatic charge on an insulating medium in a configuration corresponding to an electrode suitably biased. The electrode may be in contact with the medium or spaced therefrom during this deposition. The insulating medium may be constituted by a plastic-coated paper, predried paper, or any other dielectric sheet having a sufficiently high resistance to hold an electrostatic image at least until development is completed.

Such a recording medium designated byreference numeral 2 is shown in FIGS. 1 and 2 as supported in a recording zone generally by a backing electrode or support member 4 which holds the recording medium against contact by an electrographic stylus array 6 as it traverses the recording zone.

This array is not shown in detail but may include a linear configuration of parallel conductive electrodes suitably isolated electrically from one another. It may be mounted in or on insulative support 8 through which electrical conductors may be provided to supply electrical recording signals individually to each stylus. These electrical conductors may terminate at any suitable place on the carriage assembly in the form of a socket or othertype of electrical connection to facilitate connection to a source of recording signals such as a character generator. FIG. 2 illustrates such a place indicated by reference numeral 9.

This technique is well known in producing alphanumeric recordings where each symbol or character is composed of selected areas from a matrix of areas. For example, a five by seven matrix may be employed while a larger matrix may also be useful depending upon the quality of recorded s'ymbolsdesired.

means not shown in detail which is selectively engaged or disengaged by appropriate signals. The origin of these signals will be'described in more detail hereinafter.

Also associated with shaft 12 may be a clock motor of conventional design which is wound during the motion of the shaft 12 in a direction such as to move the stylus array from left to right as FIG. 1 is viewed. The purpose of this clock motor is to return the stylus from the right side of the recording medium 2 to the left side thereof after a left-to-right or recording traversal has been completed. As will be described in more detail hereinafter, this is a conventional technique for performing the carriage return function in the recorder. The drive pulley 14 frictionally engages a cable 16 which is supported'by idler pulleys l8 and 20 to translate the driving force of the motor 10 to the stylus support 8. To further stabilize the stylus support during its traversal of the recording medium 2, there may be provided appropriateguide shafts 22 and 24 which pass through the carriage assembly 26 to which is secured the stylus support 8. As shown through the broken away portions of FIG. 1, the carriage assembly 26 is attached to opposite ends of the cable 16 and is slidably mounted on guide shafts 22 and 24 so as to maintain the relative position of the stylus array 6 relative to the recording medium 2 during recording.

In operation the stylus array is driven from left to right across the recording medium 2 during the application of suitable recording signals to the st yli themselves. During the movement of the stylus array a predetermined amount referred to as a character space, a character is recorded on the electrographic recording medium 2 in the form of a latent electrostatic charge pattern. The recording medium 2 may be stationary in the I recording zone during the left-to-right traversal of the stylus array, during which an entire line of characters may be recorded. At the terminal'point of this stylus movement, a suitable microswitch or other means may be actuated by the presence of the carriage assembly 26 toactuate the aforementioned clutch associated with motor 10 to disengage shaft 12 from this motor. The clock motor previously referred to may then unwind expending its stored energy to the carriage assembly 26 to returnto its initial left margin position. The actuation of the switch which effects. the carriage return may also be utilized appropriately for advancing the recording medium 2 by means ofa drive roller 28.

In a situation where the just recorded information is to be rendered visible prior to incrementing the recording medium the alphanumeric shaped electrostatic charge patterns recorded by the traversal of the stylus are rendered visible by depositing electroscopic marking particles or toner on these patterns. This is accomplished in accordance with the principles of the present invention by the rotation of a developing applicator roller, or a conventional magnetic brush, etc. It is shown only schematically in the drawings since it per se forms no part of the present invention which is compatible with many donor systems.

The cylindrical developing surface 37 has as its center of radius the shaft 36 which supports the applicator 30 for rotation during the development cycle. The necessary rotative force applied to shaft 36 is provided ultimately from a suitable motor 40 having a drive shaft 42 coupled via a clutch 44 to a drive pulley 46 affixed to a shaft 48. A timing belt 50 is entrained on the drive pulley 46 and pulley 52 to which is affixed the drive shaft 36 of the applicator 30. By properly engaging the clutch 44, the applicator may be rotated in the direction of the arrows so as to move the developing surface 37 into contact with the recording medium 2 at the recording zone. This is shown with reference to the broken line 54 which illustrates the volume developed or swept out by the applicators rotation.

The applying member 32 may be made from a great number of materials, some fibrous ones of which for illustrative purposes are specified in U.S. Pat. No. 3,251,706 which issued to L. E. Walkup, May 17, 1966, which is assigned to the same assignee as the instant application. One example which works well is natural rabbit fur.

In operation toner is loaded onto the applying surface of applicator 30 via donor roller 38 and is retained by triboelectric attraction to be conveyed during the rotation of the applicator to the recording zone. At the recording zone the toner is attracted by and deposited on the latent electrostatic charge patterns placed on the recording medium 2 by the action of the stylus array in cooperation with the recording signals.

As the applicator 30 moves toward its developin g position, which can be considered as that position when its applying surface 37 is in contact with the recording medium in the recording zone, it is continually loaded by the donor roller 38. The phenomenon of loading is such that unless the applicator is deficient in electroscopic marking particles no particles will be loaded onto it by the donor roller 38. Therefore, the problem of excess toner on the applicator 30 is eliminated.

The position of applicator 30 in FlGS. l and 2 is in a non-developing position, or what may be referred to as a viewing position. Since the non-developing surface of the applicator 30 is substantially planar and passes through the axis of the shaft 36, a viewer'may directly see the recording zone without any portion of the applying member 32 obstructing his'line of vision.

The non-developing surface of applicator 30 has been referred to as planar, but more specifically it may include two planar surfaces not necessarily coplanar. Each of these surfaces extend from the shaft 36 of the applicator. If the developing surface subtended an angle of relative to the axis of rotation of the applicator, then these two planar surfaces would lie in the same plane through this axis. However, if the developing surface subtends an angle less than 180 then this non-developing surface is actually composed of two planar surfaces which are not coplanar.

The viewing position of the applicator 30 is important since it is by reason of the configuration of the applicator that immediate visual accessibility of the developed information is possible. Therefore, the viewing position should be further defined in terms of a viewing angle. As hereinabove described, the backing electrode or support 4 provides support to the recording medium 2 in a recording zone so that the linear stylus array 6 may be moved through the recording zone and uniformly with the recording medium thereat. This means that the recording zone is substantially defined by the distance between the uppermost and lowermost styli in the linear array 6 and by the margins of the recording information. Therefore, for example, if the alphanumeric symbols to be recorded have a maximum height ofone tenth of an inch and the recording medium is approximately 8 /2 inches wide then the recording zone will be approximately one tenth of an inch by a little less than 8% inches.

In order to insure uniform quality in the recorded characters, it is preferable that the backing support 4 be such as to provide a substantially flat surface at the recording zone upon which the recording medium may rest. Therefore, the latent electrostatic charge patterns recorded on the medium 2 by the moving styli can be considered to lie in a predetermined plane which is, in

' effect, a function of the position and configuration of the backing support 4. Hence, if this support 4 is substantially flat, all the electrostatic charge patterns recorded during one traversal of the carriage assembly 26 will lie in the same plane. Consequently, the viewing angle may be defined by an imaginary line (broken line 56 in FIG. 2) passing through the plane of the recording'zone which is, in effect, the plane occupied by the last-recorded symbols on the medium-2 and which is substantially perpendicular to the direction of traversal of the stylus array 6 and a line (broken line 58 in FIG. 2) extendingfrom the lower extremity of a recorded character in the recording zone and passes in close proximity to the upper most portion of applicator 30 in its viewing position. Stated another way, this second line 58 starts at the lower edge of the recording zone and extends over the top of the applicator 30 and close to it as it can be and still remain straight. As

shown in this figure, theviewing angle is approximately 45. Of course, for a greater angle, it may be desirable to reduce shaft 36 to a semicircular cross-section.

After development, the toner may be fixed to the recording medium in any of several conventional manners. For example, recording medium support and guide member 39 may house a platen fuser employing a resistance heating coil over which the medium is moved. Flash fusing or fixing may also be used to render the developed images permanent.

Having described the mechanical structure of the re corder of FIG. l and the developing system of the present invention, one possible way of controlling this re-' corder and developing system will be described with reference to the block schematic of FIG.- 3. What has been described as the recorder or printer is represented basically by the suitably labelled block 60. Theinput to the printer originates, for example, from a conventional keyboard 62 which may generate an appropriate binary code uniquely identifying the alphanumeric symbol corresponding to the actuated key of this keyboard.

' This binary code, such as used in the American Standard Code for lnformation lnterchange, is provided to the input of a conventional decoder circuit 64 which decodes the binary code to generate a character pulse on one of a series of parallel outputs indicative of the alphanumeric symbol selected at the keyboard 62. Output conductor 66 is intended to represent a number of outputs each of which would correspond to a separate,

character generator 68 which may take various conventional forms. As an example only, generator 68 may consist of a diode matrix having a number of character select input wires which corresponds to the outputs of the decoder circuit 64. These wires are selectively coupled to readout wires via diodes which are forward biased when their respective character select wire is energized. Another form which the character generator may take is a magnetic core matrix, having five columns and seven rows, wherein a particular character select wire associated with one of the outputs 66 intertwines an appropriate pattern of magnetic cores corresponding to the alphanumeric symbol to be recorded. The character generator as well as the other parts of the block diagram of FIG. 3 are not intended'to form a particular part of the present invention per se and therefore are shown schematically only since well known conventional circuits may be used to provide their functions. I

Output 70 from the decoder 64 simply provides a signal indicative of the fact that a binary code has been decoded in the decoder 64. In this manner, foreach character entered-at the keyboard 62 which effects a decoding process in the decoder 64, an outputsignal will be generated on conductor 70. This effectively provides a control pulse to the character generator which may initiate, for example, in the case of a magnetic core matrix, a distributorcircuit which would sequentially read out each column of the core matrix at a rate correlated to the speed of the styli movement. As each column is sampled by the distributor circuit, a group of parallel outputs would be energized depending on the cores set by the character select wire. The signals on these parallel outputs would be supplied to a suitable driver stage which would provide parallel recording signals to the styli in array 6 via output '71.

Additionally, the signals present on output 70 of the decoder 64 are supplied to the printer 60 and to a conventional counter circuit 72. The pulses from output 70 which are supplied directly to the printer may be used to either pulse motor 10 of FIG. 1 for a predetermined period of time necessary to move the stylus array an amount sufficient to record one character in the case of motor 10 being a stepping motor or to energize an appropriate clutch in the case where motor 10 is a constantly driving motor. There are other techniques which may be employed for energizing stylus movement other than those described herein which'are mentioned as examples only.

Counter 72 is used to indicate at its output 74 when a predetermined number of characters have been decoded by the decoder 64. In a conventional arrangement wherein each recorded line will accommodate characters, the capability of counter 72 would be such as to provide an output pulse at output 74 when acount of 80 has been'arrived at by the counter 72. This may then be used to also reset the counter to its initial condition. The output pulse from the counter 72 will be suitably delayed by a conventional delay circuit 76 for the time necessary for the stylus array to move one character space in its left-to-right direction.

In this way, delay circuit 76 will provide a signal to the printer 60 which is indicative of the fact that the 7 stylus array 6 has completed a recording traversal across the recording medium 2. This signal may be used to engage clutch 44 associated with motor 40 and timing belt 50 to effect one rotation of applicator 30. This single rotation is sufficient to result in the development of allthe latent electrostatic charge patterns provided on the recording medium 2 during the recording traversal of the stylus array 6. The use of the counter 72 in delay circuit 76 is exemplary only of one manner for timely actuating applicator 30 at the end of the recording traversal. This may also be accomplished by employing a microswitch, previously described, which is actuated by the presence of the carriage assembly 26 at the right margin of the recording medium indicating a completed recording traversal. The actuation of this switch may also be used to engage clutch 44 to effect rotation of the applicator and thereby developing the latent charge patterns. I

' Conventional techniques may be used in the case where the styli actually contact medium 2 during recording to conserve the developed information during the return of the stylus array to the left margin. Generally, this can be accomplished by slightly rotating shaft 22 and carriage assembly 26 about shaft 24 and away from the recording zone.

The electronic schematic described hereinabove is useful to actuate the applicator 30 thereby developing a line of information recorded in a single recording traversal and yet enabling direct viewing of this line of recorded information without moving the recording medium out of the way of the developer apparatus. In that situation the applicator has an axial dimension substantially the same as the width of the recording zone as measured in a direction transverse to the direction of movement ofthe recording medium. However, it is advantageous also to be able to view each recorded character as its electrostatic charge pattern is stored on the recording medium.

An apparatus which facilitates such an operation is disclosed in FIGS. 4 and v5 which show a developing member or-applicator generally designated by reference numeral 78. This applicator, in a manner similar to the applicator 30 previously described, has a developing surface 80 which is cylindrical in nature with a centerof radius corresponding to theaxis of rotation of the applicator and the shaft 82.

This shaft is provided with a keyway 84 along its entire length which cooperates with a spline 82 fixed to the support 88 of the developing surface 80 of the applicator. This support 88 has the bore therein which co operates withshaft 84 to permit the applicator 78 to slidably ride on this shaft. The spline-keyway arrangement permits the shaft 84 to control the position of the applicator about the center-of shaft 84.

A stylus support 90 is affixed to a carriage assembly 92 in a relationship similar to elements 8 and 26 previously described in connection with FIGS. 1 and 2. The carriage assembly has a bore which accommodates guide shaft 94 to further stabilize the applicator, the

stylus support and the carriage assembly. The carriage assembly 92 is also stabilized by shaft 84 which cooperates with a bore inthe extension 'of the applicator support 88 to which carriage assembly 92 is also fixed.

FIG. 5 demonstrates the viewability of recorded and developed alphanumeric characters with the applicator 78 in its viewing position. In this figure, the carriage assembly 92 is broken away as well as the stylus support so that shaft 94 is not illustrated. The applicator is on the trailing edge of the styli since, as FIG. 5 is viewed, the carriage assembly 92 moves from left to right during the recording traversal.

The direct lineof vision to the developed characters is substantially parallel to the non-developing planar surface of applicator 78. The developing surface 80 is illustrated as having an axial width of slightly greater than two character spaces. However, this width can be narrowed to any width but practically a width equal to one character space is a preferred lower limit.

The cross-sectional view of FIG. 2 effectively is the same for the embodiment of the applicator illustrated in FIGS. 4 and 5. The stylus support 8 and carriage assembly 26 are different from the similar elements in FIGS. 4 and 5 but the relationship between the recording zone and the applicator are substantially the same for the narrower applicator 78.

In operation, it is preferred that the applicator 78 be advanced through its developing cycle each time a character shaped charge pattern is layed down on recording medium 2. Referring briefly to the block diagram of FIG. 3, this can be accomplished by opening switch 96 and closing switch 98. This effectively routes those output pulses at lead 70 directly to the delay circuit 76 each time a character code is decoded in the decoder 64. Again, the delay provided by circuit 76 is necessary to permit the stylus array to traverse one character space while being energized by recording signals from the character generator 68. At the end of this delay, clutch 44 is engaged to effect the rotation of the applicator 78. For the narrower applicator 78, however, the delay afforded by circuit 76 is not essential so that the output 70 may be directly coupled to clutch 44. In this way, the charge pattern is developed as it is recorded since the path of the applicator 78 during the developing cycle is very close to the trailing edge of the stylus array on support 90.

Comparing FIGS. 4 and l, shaft 84 is analogous to shaft 36 and guide shaft 94 is analogous to guide shaft 24. Comparing FIGS. 1 and 4-further, shaft 84 in the embodiment of FIG. 4 is serving a dual role which was divided in the apparatus of FIG. 1 between guide shaft 22 and applicator shaft 36.

The viewing angle defined hereinabove in connection with FIG. 2 is substantially the same as the viewing angle afforded by the narrower applicator 78 and consequently the view illustrated in FIG. 5 of the developed characters is the same as an operator would have with the full width applicator 30.

A specific applicator configuration has been illustrated in the embodiments of FIGS. 1 and 4. However, it can be appreciated that other configurations are possible within the inventive concept described herein. For example, while the angle subtended by the developing surface has been illustrated as being or slightly less, this angle may be reduced or increased considerably depending upon the radius of the cylindrical developing surface. The limiting factor on the angle subtended by the developing surface is in the first instance 0f the radius of curvature of this cylindrical surface.

This factor is dictated by the necessity for high quality development of passing a certain predetermined amount of developing surface across the latent electrostatic charge patterns to be developed. With a larger radius the developing surface maybe the same for an angle of, say, 30 as it would be using a smaller radius where the cylindrical surface subtends a 180 angle.

In addition, the configuration of the developing surface need not necessarily be cylindrical in the sense of having the same radius for every point on the developing surface. For example, the applicator may have a short flat surface or may be an ellipsoid, or portion thereof, which can be defined as the volume of a'surface all plane sections of which are ellipses as well as circles. An ellipse, for purposes of this description'and the appended claims, may be defined as a closed plane curve generated by point moving in such a way that the sums of its distances from two fixed points is a constant. Therefore, cylindrical is intended to describe the surface, or any portion thereof, of an ellipsoid. As may be expected from the description of the present invention, the axis of rotation of the applicator may be at a position other'than its geometric or physical center.

Regardlessof the configuration, the center of rotation of the applicator, i.e., the axis of shafts 36 and 82, will be a distance from the recording zone which is less than the distance from this axis to the most remote point of the developing surface. This insures that, as the applicator rotates, the developing surface will contact the recording medium in the recording zone. 7

Further, although reference has been made to conventional toner, electroscopic marking partieles'suspended in a suitable liquid may also be used where the applicator is a suitable absorbent or porous material. Therefore, such techniques as described in US. Pat. No. 3,096,198, which issued to R. M. Schaffert on July 2, 1963. may be employed with an applicator configured as described herein in accordance with the principles of the present invention.

In addition, although a fibrous applicator has been illustrated, a magnetic brush may be used in accordance with the inventive concepts described hereinabove with the inventive configuration to permit maximum visual accessibility. The same is true of other suit able developing techniques compatible with the applicator configuration hereinabove described such as a dry toner loaded gravure surface.

Furthermore,- while the present invention has been described in conjunction with an electrographic recorder, other applications are possible such as rapid development'of slit exposed xerographic plates.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. 1

What is claimed is: r

1. In a recording apparatus having means for advancing a recording medium through a recording zone and means for moving 'an electrostatic image-forming member through said recording zone in a direction substantially transverse of the direction of the movement of said recording medium, the improvement comprising:

an applicator and means for rotatably supporting said applicator opposite said recording zone, said applicator comprising developing and non-developing surface means, said developing surface means being capable of holding developer; and

means for rotating said applicator between developing and non-developing positions to thereby present the developer held by said developing surface means to said record medium when in the developing position and for permitting viewing of developed images when in the non-developing position.

2. Apparatus according to claim 11 wherein said developing surface means has an arcuate configuration subtended by an angle of less than 360 from said sup- 5. Apparatus according to" claim 1 wherein said' means for rotating said applicator comprises means for incrementally and continuously rotating said applicator.

6. Apparatus according to claim 1 including means for supporting said applicator for movement transverse to said recording medium.

7. Apparatus for. rendering visible electrostatic charge patterns placed on a recording surface movable through a recording zone comprising:

an applicator capable of retaining electroscopic marking particles; 1

means for supporting said applicator for rotation about anaxis; means for rotating said applicator about said axis between developing and non-developing positions whereby in said developing position electroscopic marking particles are presented to said charge patterns and in said non-developing position said applicator does not obstruct viewingof developed images; and

means for supporting and moving said applicator'for movement transverse ofthe direction of movement of said recording surface.

8. Apparatus according to claim 7 wherein said means for rotating said applicator comprises means for effecting incremental rotation each time a pattern is placed on-said recording medium.

9'. Apparatus according to claim 8 wherein said applicator comprises fibrous material.'

10. An applicator for applying electroscopic marking materials to a recording medium in a zone in a first position and for allowing visual accessibility to said zone in a second position comprising:

a shaft defining an axis of rotation parallel to the surface of said recording medium;

fibrous material capable of retaining electroscopic marking particles mounted on said shaft and including fibers extending substantially in a radial direction relative to said axis, the locus of the free ends of said fibers forming a substantially arcuate surface; means for supporting said shaft such that said axis is a distance from said zone which is less than the distance of the most remote point of said arcuate surface from said axis; and

motive means coupled to said shaft for rotating said 

1. In a recording apparatus having means for advancing a recording medium through a recording zone and means for moving an electrostatic image-forming member through said recording zone in a direction substantially transverse of the direction of the movement of said recording medium, the improvement comprising: an applicator and means for rotatably supporting said applicator opposite said recording zone, said applicator comprising developing and non-develoPing surface means, said developing surface means being capable of holding developer; and means for rotating said applicator between developing and nondeveloping positions to thereby present the developer held by said developing surface means to said record medium when in the developing position and for permitting viewing of developed images when in the non-developing position.
 2. Apparatus according to claim 1 wherein said developing surface means has an arcuate configuration subtended by an angle of less than 360* from said support means.
 3. Apparatus according to claim 1 wherein said developing surface means comprises an arcuate configuration formed by an angle of substantially 180* subtended from said support means.
 4. Apparatus according to claim 3 wherein said developing surface means comprises a fibrous material.
 5. Apparatus according to claim 1 wherein said means for rotating said applicator comprises means for incrementally and continuously rotating said applicator.
 6. Apparatus according to claim 1 including means for supporting said applicator for movement transverse to said recording medium.
 7. Apparatus for rendering visible electrostatic charge patterns placed on a recording surface movable through a recording zone comprising: an applicator capable of retaining electroscopic marking particles; means for supporting said applicator for rotation about an axis; means for rotating said applicator about said axis between developing and non-developing positions whereby in said developing position electroscopic marking particles are presented to said charge patterns and in said non-developing position said applicator does not obstruct viewing of developed images; and means for supporting and moving said applicator for movement transverse of the direction of movement of said recording surface.
 8. Apparatus according to claim 7 wherein said means for rotating said applicator comprises means for effecting incremental rotation each time a pattern is placed on said recording medium.
 9. Apparatus according to claim 8 wherein said applicator comprises fibrous material.
 10. An applicator for applying electroscopic marking materials to a recording medium in a zone in a first position and for allowing visual accessibility to said zone in a second position comprising: a shaft defining an axis of rotation parallel to the surface of said recording medium; fibrous material capable of retaining electroscopic marking particles mounted on said shaft and including fibers extending substantially in a radial direction relative to said axis, the locus of the free ends of said fibers forming a substantially arcuate surface; means for supporting said shaft such that said axis is a distance from said zone which is less than the distance of the most remote point of said arcuate surface from said axis; and motive means coupled to said shaft for rotating said applicator about said axis and to said first and second positions; said arcuate surface being substantially equidistant from said axis and subtending an angle relative thereto of substantially 180*. 